The present invention relates to a threading device of sewing machine, and more particularly relates to a threading device for guiding the upper thread smoothly and exactly into engagement with a thread holder while the threading device is operated to pass the upper thread through the needle eye of a machine needle, the upper thread being extended from a thread supply provided on the sewing machine and thread holder being provided to hold the upper thread between the thread supply and the machine needle.
So far, many inventions have been made in connection with a threading device of sewing machine. According to the conventional threading device, a threading shaft is vertically moved down along a guide groove in association with downward movement of an operating member and is stopped at a place where there is a needle eye. With further movement of the operating member, the threading shaft is axially rotated.
In association with the axial rotation of the threading shaft, a threading hook is moved to pass through the needle eye toward the user from the rear side of the needle. Then the user hangs the upper thread onto the threading hook, the upper thread extending from a thread supply provided on the sewing machine.
With release of the operating member or by moving up the operating member, the threading shaft is moved up and the threading hook is pulled out of the needle eye while the upper thread is passed through the needle eye. Thus the threading operation is finished. In this connection, it is general that the thread holder is mounted to the needle bar to hold the upper thread between the thread supply and the needle. It is also general that the upper thread is manually hung onto the thread holder before the upper thread is passed through the needle eye. However, in fact, it is considerably difficult to manually hang the upper thread onto the thread holder. Moreover, the user may often forget to hang the upper thread onto the thread holder. A device for solving such problem is disclosed in the Japanese patent application laid open Hei 9-192381.
However, the device disclosed in the Japanese patent application is extremely complex with many parts required. The device further requires high precision in assembling the parts, but is poor in endurance.
According to the device disclosed in the Japanese patent application, with release of the operating member 25 from pressure, the threading hook 8a is pulled out of the needle eye 12a. Then the thread which is caught by the threading hook 8a may be passed through the needle eye 12a in a form of loop. However, as the threading hook 8a is moved up, the threading hook 8a often fails to hold the thread loop which is not sufficiently tensed and may get out of the threading hook 8a. The thread loop freed from the threading hook 8a may be often disengaged from the needle eye 12a due to some shock or impact accidentally produced or by some mistake of the user.